shell: doom timeout exception should include argv[0], jobid of affected job

[grondo]

The exit-timeout exceptions have been somewhat confusing to users because when they pop up in a batch job error log, it isn't immediately clear which job hit the exit timeout.

It might be useful to include the basename of the task that exited (i.e. was it flux-broker or my task?) and the jobid so it is clear the exception occurred on a job within the batch job, not the batch job itself, etc.